This invention relates generally to peak demand control on utility electrical systems, and more particularly concerns the reduction of a secondary peak of power drawn by a number of distributed electrical loads using energy storage equipment.
Prior art U.S. Pat. Nos. 3,906,242, 4,023,043, 3,630,275, and 3,422,248, hereby fully incorporated by reference, disclose methods of controlling peak loads on electrical utility distribution systems, and stored energy electrical heating apparatus respectively. Operation of the above mentioned apparatus has been highly satisfactory and many units are in operation, effectively providing utilities with an "interruptable" load for pre-determined periods. Use of this type of heater allows the electrical utilities to essentially even out demand over a twenty-four hour period. This reduction in demand "peaks" results in substantial financial savings to the utilities in that extra generating capacity need not be installed, or higher cost "peaking" power need not be used.
The central control systems disclosed in U.S. Pat. Nos. 3,906,242, and 4,023,043, however, have not found wide use due to the difficulties involved in maintaining individual signal responsive equipment located at the site of each stored energy heater.
Therefore, it has become common practice to control the power-off period of individual stored energy loads through the use of a simple time clock attached to each unit providing cycles of power-on and power-off periods. "Power-on" periods are usually in the range of four to twelve hours in a twenty-four hour period although other cycles are used, some having more than one "power-on" period in 24 hours.
However, if a substantial number of units are connected to a given utility system it has been found that after a power-off period, a high percentage of the storage loads are operating at reduced temperature due to the heat draws during the power off interval. If a simple temperature controller is utilized to establish a maximum limit in the energy storage, at the conclusion of each power-off period, a large number of units will be connected to the utility lines thereby producing what has become known as a "secondary peak".
Secondary peaks, while greatly reduced from the prior or primary peak, are still undesirable.
Therefore, it is the object of this invention to provide a controller which utilizes the existing stored energy temperature, and the ambient temperature, in a predetermined combination to provide a diversity of power demands among a plurality of geographically distributed stored energy heaters connected to a utility system.
It is a further object of this invention to provide a method for reducing "secondary peaks" on an electrical utility through the use of a self-contained, self-operating controller which automatically adjusts the power requirements of the individual stored energy heater to minimize the power draw after a substantial power-off period.
It is a still further object of this invention to provide a method for controlling secondary peaks which is locally adjustable to individual loads and thereby provides substantial diversity in overall power requirements for a plurality of connected stored energy heaters on a given utility distribution system.
It is an additional object of this invention to provide a controller for a stored energy electrical heater which continuously measures the storage temperature, ambient temperature, and provides self-determined adjustment of the unit power requirements after a substantial "power-off" period.
It is a further object to this invention to provide a controller embodying the above objects and further utilizing micro-computer techniques to provide additional control of tank storage temperature and power consumption through improved estimation of heating requirements in a follow-on "power-off".